The present invention concerns an electronically commutated motor and a method for operation of this motor according to the preamble of independent patent claims 1 and 9.
For the sake of simplicity and for better understanding, a three-phase motor excited by a permanent magnet is primarily discussed in the description, whose phases are arranged in known fashion. The present invention, however, is not restricted to a variant with three phases, but is fully applicable to variants with more than three phases and/or more than one permanent magnetic pole pair.
The drive signals for the individual phase are generated by corresponding position sensors. Hall elements or Hall ICs are preferably used according to the prior art as position sensors. The mutual rotation angle spacing or spacing of the individual Hall sensors relative to each other stated in radians is dependent on the number of magnetic pole pairs, the exact commutation times only being guaranteed when the spacing tolerance of the position sensors equals zero. Under practical conditions this requirement cannot be achieved, so that current supply of the phase windings driven by the corresponding Hall sensors occurs either too early or too late.
Such incorrect commutations result in an increase in torque ripple of the motor, which, on the one hand, leads to intensified vibrations and, on the other hand, hampers exact position or torque control.
Positioning accuracy for the Hall sensors of xc2x10.1 mm can only be accomplished at extremely high cost and satisfies the requirements less, the more the sensor system of the motor is miniaturized.
This problem is much more strongly pronounced in particular in motors with a larger number of pole pairs, since in this case, the mechanical angular spacing corresponding to a xe2x80x9celectricalxe2x80x9d rotational angle, under which the Hall sensors must be arranged, becomes increasingly smaller.
In particular, when the outside dimensions of these motors become increasingly smaller in adjustment to corresponding incorporation conditions so that the radius of the circle on which the Hall sensors are arranged also diminishes, the resulting percentage angular error resulting from this is increased at the same positioning accuracy. The smaller the motor and the larger the number of magnetic pole pairs, the more critical the position tolerances of the Hall sensors are as angle errors with reference to the commutation times of the corresponding phase windings.
The underlying task of the invention is therefore to generate commutation signals produced by Hall sensors more precisely and less subject to tolerance so that commutation is no longer dependent on the corresponding dimension-related scatter with reference to arrangement of these Hall sensors on the circuit board.
The solution to this task occurs with the technical teachings of the independent patent claims 1 and 9.
It is important according to the invention that only the output signals of a single position sensor are evaluated as signal source after startup of the motor. Startup occurs, as previously, with allowance for the tolerance-burdened output signals of at least two position sensors operating with the same timing frequency.
All additional commutation times are derived from the timing frequency of this one signal source, in which the timing frequency of this one signal source is a whole number multiple (corresponding to the number of phases) of the second frequency with which the other position sensors necessary for motor startup conforming to direction of rotation are driven. An additional Hall sensor can be provided as signal source with higher timing frequency, which is driven via an additional magnetic track with a correspondingly higher number of pole pairs. The higher timing frequency, however, can also be derived from one of the position sensors operating with lower timing frequency whose low timing frequency is prepared and multiplied accordingly by a method of signal technology appropriate for this.
The Hall sensors are arranged on a fixed circuit board, whereas the control magnetic disk rigidly connected to the rotor rotates at spacing Z1 around the common Z axis. In the case of an additional Hall sensor H4, the Hall sensors H1, H2 and H3 are arranged on an arc around Z with radius R1 by 30xc2x0 mechanical (corresponding to 60xc2x0 electrical), in which R1 corresponds to the average radius of the inner magnetic track 1 (two pole pairs). The additional Hall sensor H4, for example, is arranged diametrically to H2 on an arc with radius R2, in which R2 corresponds to roughly the average radius of the outer magnetic track 2 (3xc3x972=6 magnetic pole pairs).
For example, if the Hall sensor is switched from a north pole at logic xe2x80x9c1xe2x80x9d and accordingly from a south pole at logic xe2x80x9c0xe2x80x9d, a state diagram still to be explained in the later drawings is obtained during rotation of the control magnetic disk. Since one can establish immediately after the first state change by means of a truth table whether the motor is rotating in the desired direction, the Hall sensor H4 timed with the higher frequency can be switched to shortly after startup of the motor, but at the earliest after the first state change.
After switching the commutation times are exclusively stipulated by the output signal of Hall sensor H4. This state can be maintained until the motor is stopped again. However, it is important that before restartup, i.e., at the latest during shutdown, the state signals of the other Hall sensors must be reactivated so that during the next startup of the motor the actual rotor position can be clearly verified. To be able to guarantee this, the signals of the other Hall sensors H1-H3 must also be evaluated in this operating state.
It is therefore proposed according to the invention in a first approach to the solution, starting from the prior art, to provide a fourth Hall sensor H4 and a second control magnetic track in order to be able to derive the exact commutation times from the higher timing frequency of the additional Hall sensor.
It is recognized from the resulting truth table that in a three-phase motor excited by a permanent magnet only three Hall sensors are required in principle for distinct position and directional rotation recognition. In addition to Hall sensor H4 with the higher timing frequency and an additional second control magnetic track, only two additional Hall sensors, for example, H2 and H3 are therefore required instead of the initially proposed three Hall sensors H1, H2 and H3. This solution is more cost effective, since overall, according to the prior art, only three Hall sensors are again used. In this case the motor is started with H2, H3 and H4 and after starting, at the earliest after the first phase change, only H4 is evaluated.
From this point, the signals of the other Hall sensors are therefore no longer considered so that the commutation times are stipulated free of tolerance merely by the phase change of Hall sensor H4. Driving of the power transistors that switch the coil currents occurs, for example, via an upline xcexc processor.
It is therefore proposed according to the invention in the second approach to the solution to use the minimum number of position sensors from the prior art, but in which one of these position sensors is arranged on an arc with a different, for example, larger radius and is driven via a second magnetic track with a correspondingly higher number of pole pairs. This position sensor then delivers the higher timing frequency required for determination of the exact commutation times.
In a third approach to the solution according o the invention, it is proposed to derive the higher timing frequency required for determination of the exact commutation times by an appropriate and known method of signal technology for the timing frequency of a position sensor H1 or H2 or H3 driven with the usual low timing frequency, for example, by frequency multiplication.
The invention is now characterized by the fact that the state signals of all Hall sensors are evaluated for starting of the motor, but that after startup of the motor commutation is still only triggered by the state signals of a single Hall sensor. A new method is therefore involved, characterized by the fact that in the first phase the relatively dimension-dependent and therefore, error-burdened commutation signal for startup of the motor are obtained from a number of Hall sensors offset relative to each other in the plane and the commutation signals are still only obtained from a single Hall sensor at the earliest after the first state change of one of the Hall sensors, whereas the signals generated by the other Hall sensors remain unconsidered. It is therefore important that after startup only a single Hall sensor is responsible as timing sensor for commutation of the motor. Position-tolerance-dependent scatter of the commutation signal is therefore avoided because only the state signals of the single Hall sensor are evaluated for commutation of the motor.
In a variant of the motor with three phases, three or more sensor signals are thus evaluated, from which an at least three-figure digital code is formed. This digital code is the reference for the phase position in which the rotor is situated relative to the stator.
At the starting time an arbitrary specified code is present, for example 1-0-0. With reference to a specific stipulated or intended desired direction of rotation, however, one also knows which codes follow next after the rotor has been placed in motion.
With opposite direction of rotation of the rotor, these codes would be issued in the opposite direction.
After the actual code for the shutdown position is recognized after query and evaluation of the state signals produced by the Hall sensors, the neighboring and all subsequent codes are also known, in which, depending on the direction of rotation, one position of the code is changed with each state change and the corresponding next code is thus generated.
It is explained below that the described principles apply not only to a three-phase motor, but also to motors with more than three phases. However, the different feed possibilities of three-phase motors are initially explained:
In principle, it applies that a three-phase motor with bipolar driving requires six different states in driving the phases. A six-pulse motor is involved accordingly. The employed number of pole pairs now states after which mechanical rotor rotation angle a full electrical cycle is traversed in which every 60xc2x0 electrical corresponds to 30xc2x0 mechanical. Similar ratios apply in multiphase motors with more than three phases.
During commutation of a three-phase motor with two pole pairs, a sequence of six different codes is therefore required corresponding to the six different state changes pertaining to an electrical cycle (one cycle equals 360xc2x0 electrical corresponding to 180xc2x0 mechanical or a half rotation).
The object according to the invention of the present invention is apparent not only from the object of the individual patent claims, but also from the combination of individual patent claims.
All data and features disclosed in the documents, including the summary, especially the spatial layout depicted in the drawings, are claimed as essential to the invention if they are new separately or in combination relative to the prior art.
The invention is further explained below by means of drawings showing several variants. Additional features essential to the invention and advantages of the invention are apparent from the drawings and their description.